Manufacture of magnetic bodies from compressed powdered materials



Patented Nov. 28, 1950 UNITEDy STATES PATENT OFFICE MANUFACTURE OF MAGNETIC BODIES FROM COMPRESSE!) POWDERED MA- TERILALS No Drawing;

Application December 19, 1946, Se-

rial No. 717,330. In Great Britain November 3 Claims.

This invention relates tothe manufacture of magnetic bodies Jfrom compressed powdered materials.

The principal object of the invention is to, elfeet a reduction in the energy losses in such bodies;

In an article in the Bell System Technical Journal, volume l (1936) entitled Magnetic Measurements at Low Flux Densities it is shown (page 49) that the losses in a coil corer are represented by an equation R =Ma3m+0 f+uef2 wherein R is the resistance in ohms flue to core and Winding only and L is the inductance in henries due t0 coreand residual air space only. The terms on the right hand side oi this equau tion may be considered as different loss cecilicients, and as proportional to constants 1:31, K2 and Ke Where KlI/LCX 103 where u is the permeability of the body, o is the hysteresis resistance coellicient, c is the esidual resistance coelicient and e is the eddy current resistance coeiiicient of the core, as defined in the aforesaid article. K1 is known as the residual loss coeilicient, K2 the hysteresis comeicient and Ke the eddy current coefficient.

The present invention has for its principal object to effect a reduction in the hysteresis coellicient K2 more particularly, though wet exclusively, in magnetic bodies that are use in carrier current transmission systems, especia-1137 hign frequencies. The presence oi the liyste loss coefficient K2 causes the generation o liarlsionic voltages and thus a reduction thereolC means a reduction of the intermodulation between diiferent channels of transmission, and simplification of circuit problems arising from resistn ances which vary with energy level. The present invention has also beeL found to provide some reduction in the loss coeiilcient B11.

The eddy current coe lent l@ is solely dependent on the particle size of tbe powder and providing the particles are adequately insulated from one another it cannot be altered for a given particle size. Hence lor a given particle size the only variables that can be altered are K1 and K2.

According to the present invention the hysten resis loss coefcient is reduced considerably be- (Cl. B52-62.5)

low values previously attained by the use of silica sol as a primary insulating layer for the magnetic particles.

It is preferable to use as a secondary insulating layer applied outside the primary insulating layer a na-rd dense non-plastic insulant such as titanium dioxide.

The best results have been obtained by the use or an insulation that consists of three layers applied successively to the particles the lirst cornprising silica sol, the second magnesium liydroxide and the third titanium dioxide. The use of the titanium di ride forms the subject matter of our coapending Application No. 717,329, filed December 19, 1946.

It is believed that these results may be explained on the theory that the minimum hysteresis coefficient is obtained when the magnetic particles bave been subjected to the maximum plastic deformation Without the particles having been brought into contact with one another. Silica sol forms a primary insulatingv layer which has the property of flowing under the pressure which is used to compr ss the particles into core iorrn whilst retaining enveloping insulating film over each particle.

The plastic deformation taires place under the pressure used for the purpose of c pressing the insulated magnetic particles into a solid an annealing of the solid body is necessary to cause re-crystallisation in the magnetic material. The greater the plastic deformation the lower the re-cristallisation tempera tire for a given magnetic material and the greater is the freedom from strain in the magnetic which is well known to be desirable.

The primary layer of silica. sol is of such a character that minimum volumetric change occurs during subsequent processes so that the magnetic particles are not in a e or strain after heat-treatment. Moreover silica soi ha. a low power factor and this assists i; lowering the 2 constant.

The following description relates to embodiments of the invention. in which the magnetic particles consist oi alloy containing S%-? nickel, M-19% iron up to nioly'bd and of such size as to a 460 mesh scr When suele particles are to be compressed into bodies for use with carrier currents the amount oi" insulation used ornially sue that the meability of the iinished core is about 14.

'line best results hitherto wit-n cores of permeability 14 made from powder of the above composition and fineness have been obtained by means of insulation consisting of colloidal clay, such as kaolin, magnesium hydroxide and sodium silicate as described and claimed in British speciiication No. 438,803, with the addition of a small percentage of a phenol formaldehyde resin according to British application No. 16407/44. The insulated particles are pressed into cores under a pressure of 45 tons per square inch and then annealed in an inert atmosphere `at 630 C. for 40 minutes.

The properties obtained from the nished cores are a permeability of 14, K2=0.10, K1=2.70 and Kia-:0.07. In the following examples the cores are manufactured in the same manner save for the nature of the insulation used.

Example 1 100 parts of the magnetic dust are thoroughly mixed with 10 parts of silica sol; and the mixture dried at 50 C. and passed through a 120 mesh sieve. The insulated dust that passes the sieve is thoroughly mixed with 2% parts of magnesium hydroxide in aqueous suspension. The resulting mixture is evaporated at 130 C. to dryness with continuous mixing and screened through a 30 mesh sieve. The material passing the sieve is compressed into a core which has a permeability of 14.05 and a K2 of 0.07.

Example 2 Same as Example 1 except that 5 parts of magnesium hydroxide are used. The permeability is decreased to 10.9 and the K2 also increased to 0.11.

It appears that there is an upper limit to the quantity of magnesium hydroxide that can be used without unduly increasing the factor K2.

Example 3 100 parts of magnetic dust are mixed with 10 parts of silica sol, dried at 50 C. and passed through a 120 mesh sieve. 1.25 parts of magnesium hydroxide in aqueous suspension are thoroughly mixed with the material passing the sieve and the mixture evaporated to dryness at 130 C. 4.6 parts of titanium dioxide are dry mixed therewith and the result screened through a 30 mesh sieve. Cores made from this compressed material have a permeability of 13, a factor K2 of 0.064; a factor K1 of 1.2 and a factor Ke of 0.06.

The use of titanium dioxide is described and claimed in our co-pending application No. 717,329 of even date herewith.

The results obtained by Example 3 are considered to be the best obtained for a permeability in the neighbourhood of 14, as al1 loss factors show some decrease, and that in the factor K2 showing a 40% decrease.

The following examples relate to cores intended for use at still higher frequencies than the foregoing and thus intended to have a permeability in the neighbourhood of 6.

Example 4 100 parts of magnetic dust are thoroughly mixed with 10 parts of silica sol, dried at 50 C. and screened through a 120 mesh sieve. The material passing the sieve is mixed with 5 parts of magnesium hydroxide in water suspension and the mixture dries at 130 C. The dried material is thoroughly mixed with 6 parts of magnesium oxide powder and 2 parts of a phenol formaldehyde resin. This mixture is heated at 40 C. for

half an hour and screened through a 30 mesh sieve. The material passing the sieve is compressed into cores. The permeability is 6.9 and the factor K2 0.062.

Eample 5 Same as Example 4 as regards the rst two coatings. The dried mixture with magnesium hydroxide is mixed with 15 parts of titanium dioxide and 2 parts of a phenol formaldehyde resin. The mixture is passed through a 30 mesh sieve, semi-cured at 40 C. and the material passing the sieve compressed into cores. The permeability was 5.8 and the factor K2 was 0.046. The factor K1 was 2.0 and Ke was 0.045 thus showing a decrease in all three loss factors compared with normal type insulation.

One method of preparing the silica sol was to hydrolise a commercial form of silicon ester in methylated spirits by means of hydrochloric acid solution (0.5 N in distilled water). In the following claims this type of silica sol is referred to as acid hydrolyzing silicon ester which will be understood by those skilled in the art to which this invention relates as being that type of substance produced by acid hydrolysis of an alkyl orthosilicate, for instance ethyl orthosilicate, hydrolyzed with methyl alcohol or a similar lower alcohol containing an aqueous acid solution.

What is claimed is:

1. Method of manufacturing a body having low hysteresis loss factor from compressed insulated magnetic particles of high permeability which comprises rst insulating the particles with a primary insulating layer consisting of an acid hydrolyzed silicon ester, subsequently insulating the particles with at least one further layer of insulation comprising an intermediate layer of at least one substance chosen from the class consisting of magnesium oxide and magnesium hydroxide, and an outermost layer comprising titanium dioxide, compressing the particles so insulated into core form to cause plastic deformation of the magnetic particles and then annealing the nished core to recrystallise the magnetic particles.

2. A magnetic body composed of magnetic particles insulated from one another by a plurality of separately applied individually distinct layers of insulation compressed into a solid body in which the outermost layer comprises titanium dioxide an underlying intermediate layer comprises magnesium oxide and the inner layer comprises an acid hydrolyzed silicon ester.

3. A magnetic body composed of magnetic particles insulated from one another by a plurality of separately applied layers of insulation on said particles compressed into a solid body, said layers comprising titanium dioxide as the outermost layer, silica sol as the innermost layer and magnesium hydroxide as the intermediate layer.

WILLIAM EDWARD LAYCOCK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,669,642 Andrews May 15, 1928 1,836,746 Beckinsale et al. Dec. 15, 1931 1,881,711 Lathrop Oct. 11, 1932 2,179,810 Brill Nov. 14, 1939 Certificate of Correction Patent No. 2,531,445 November 28, 1950 WILLIAM EDWARD LAYCOCK It is hereby certified that error appears in the above numbered patent requiring correction as follows:

In the grant, line 16, strike out of Seventeen years; same line, after grant insert until N member Q3, 1.965 in the heading to the printed specification, line 1l, before 3 Claims insert Secz'ou 1, Public lla/ws 6190, August 8, 1946. Patent empires N ouember 23,1965;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the ease in the Patent Oce.

Signed and sealed this 1st day of May, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'ssoner of Patents.

Certificate of Correction Patent No. 2,531,445 November 28, 1950 WILLIAM EDWARD LAYCOCK It is hereby certified that error appears in the above numbered patent requiring correction as follows:

In the grant, line 16, strike out of Seventeen years; same line, after grant insert until November 23, 1.965 in the heading to the printed specilioation, line 11, before 3 Claims insert Section l, Public Ztl/w; 690, August 8, 1946'. Patent epz'res N Member Q3, 1.965 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent OfIice.

Signed and sealed this 1st day of May, A. D. 1951.

THOMAS F. MURPHY,

Assistant O'Ommvz'ssz'oner of Patents. 

1. METHOD OF MANUFACTURING A BODY HAVING LOW HYSTERESIS LOSS FACTOR FROM COMPRESSED INSULATED MAGNETIC PARTICLES OF HIGH PERMEABILITY WHICH COMPRISES FIRST INSULATING THE PARTICLES WITH A PRIMARY INSULATING LAYER CONSISTING OF AN ACID HYDROLYZED SILICON ESTER, SUBSEQUENTLY INSULATING THE PARTICLES WITH AT LEAST ONE FURTHER LAYER OF INSULATION COMPRISING AN INTERMEDIATE LAYER OF AT LEAST ONE SUBSTANCE CHOSEN FROM THE CLASS CONSISTING OF MAGNESIUM OXIDE AND MAGNESIUM HYDROXIDE, AND AN OUTERMOST LAYER COMPRISING TITANIUM DIOXIDE, COMPRESSING THE PARTICLES SO INSULATED INTO CORE FORM TO CAUSE PLASTIC DEFORMATION OF THE MAGNETIC PARTICLES AND THEN ANNEALING THE FINISHED CORE TO RECRYSTALLISE THE MAGNETIC PARTICLES. 